Answer
Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
As for your query, one sheep is sufficient only for a man and his family while a cow or a camel is sufficient for one to seven families.
Responding to your question, Sheikh M. S. Al-Munajjid, a prominent Saudi Muslim lecturer and author, states:
One sheep is sufficient as a sacrificial animal for one man and his family and whoever he wants among the Muslims, based on the Hadith of Aishah (may Allah be pleased with her), who said that the Prophet (peace and blessings be upon him) ordered that a ram with black legs, black belly and black (circles) round the eyes should be brought to him so that he could sacrifice it. He said to Aishah, “Give me the knife,” and she did that. He took it, then he took the ram, placed it on the ground and then slaughtered it (i.e., prepared to slaughter it), saying, “In the name of Allah, O Allah, accept (this sacrifice) on behalf of Muhammad and the family of Muhammad and the Ummah of Muhammad.” Then he sacrificed it. (Muslim)
It was narrated that Abu Ayyub Al-Ansari (may Allah be pleased with him) said, “At the time of the Prophet (peace and blessings be upon him), a man would sacrifice a sheep on behalf of himself and his household, and they would eat some and give some to others (Ibn Majah and At-Tirmidhi)
If a man sacrifices a single sheep or goat on behalf of himself and his family, that will suffice for everyone he intended of his family, whether living or deceased. If he did not intend anything specific, then it includes all those who are included in this word (family or household), either customarily or linguistically.
Customarily, it refers to all those whom he supports of wives, children, and relatives; linguistically, it includes all those who are related to him of his own children and the descendants of his father, grandfather, and great-grandfather.
One-seventh of a camel or a cow is equivalent to one sheep. If a man sacrifices one-seventh of a camel or cow on behalf of himself and his family, that is sufficient because the Prophet (peace and blessings be upon him) said that one-seventh of a camel or a cow takes the place of one sheep in the case of the hadi (sacrifice offered during Hajj), so that applies also to the Udhiyah because there is no difference between the Udhiyah and the hadi in this regard.
If two or more people buy one sheep and sacrifice it, it is not sufficient, because no such thing has been narrated in the Quran or the Sunnah. Similarly, if eight or more people share one camel or one cow, that is not sufficient (but it is permissible for seven people to share a camel or a cow), because acts of worship are as prescribed in the Quran and Sunnah and are not subject to personal opinion; it is not permissible to go beyond the set limits with regard to how much is to be done or the way in which it is to be done.
This does not have to do with including others in the reward because it was narrated that there is no limit to the number of people on whose behalf the sacrifice may be offered.
Allah Almighty knows best.
Editor’s note: This fatwa is from Ask the Scholar’s archive and was originally published at an earlier date.
Source: www.islamqa.info